The population genetics of copia-like transposable elements in Drosophila will be investigated, with special reference to their ability to be transferred horizontally among species and their extent of sequence divergence among related species. Three specific aims will be pursued: 1. Heterologous transformation will be developed in order to transfer transposable elements among species. Initially, the P-element-mediated rosy transformation system will be used to transform D. simulans with DNA from D. melanogaster. Successful transformation will establish the ability of P to transpose in genomes other than that of D. melanogaster. Subsequent experiments will determine how widely among Drosophila species this element can be disseminated and still remain transposable. In addition, P-bearing cotransformants will be studied in order to determine whether hybrid dysgenesis, a complex syndrome of germ-line abnormalities associated with P element in D. melanogaster, also occurs in other species into which P has been introduced. These experiments will provide information about host-element interactions in transposition, and they will permit evaluation of the postulated role of P-like elements in speciation. 2. A highly unstable white allele in D. mauritiana will be studied genetically and at the molecular level to characterize an inserted DNA element. This mutant is of interest because D. mauritiana and D. simulans have many fewer copia-like elements than their sibling species D. melanogaster. Transposable elements that are retained in D. mauritiana and D. simulans may therefore have certain unusual properties. These studies may explain why transposable elements of a given family are not distributed among species as would be expected from their phylogenetic affiliation. In the long run the unstable white allele will be transformed into D. melanogaster in order to study its mutational characteristics in an alien genome. 3. The transposable element copia will be studied among related species of Drosophila in order to determine the extent of restriction-map variation within and among species. Several copias differing in restriction map occur in D. melanogaster, and copia in D. mauritiana differs from that in D. melanogaster. Our studies will focus on strains collected relatively recently. These studies will reveal whether concerted evolution occurs in dispersed repeated multigene families, which will be important in evaluating the relative role of the evolutionary forces that impinge upon such elements.